CVE-2026-45028

References

• Fix PR: https://github.com/withastro/astro/pull/16457
• Example demonstrating the vulnerability: https://github.com/CyberSecurityAustria/ACSC2026-web-astronomical

Astro versions prior to 6.1.10 used AES-GCM encryption to protect the confidentiality and integrity of server island props and slots parameters, but did not bind the ciphertext to its intended component or parameter type. An attacker could replay one component's encrypted props (p) value as another component's slots (s) value, or vice versa.

Since slots contain raw unescaped HTML while props may contain user-controlled values, this could lead to XSS in applications that meet all of the following conditions:

• The application uses server islands
• Two different server island components share the same key name for a prop and a slot
• An attacker has full control over the value of the overlapping prop (requires a dynamically rendered page)

These conditions are very unlikely to occur in real-world production applications.

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-45028 has a CVSS score of 6.1 (Low). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (6.1.10); upgrading removes the vulnerable code path.

Kodem intelligence

This has been patched in [email protected].

The fix binds each encrypted parameter to its target component and purpose using AES-GCM authenticated additional data (AAD). Each ciphertext now includes context like props:IslandName or slots:IslandName, so encrypted data for one component cannot be replayed against a different component, and encrypted props cannot be reused as slots.

1. What is CVE-2026-45028? CVE-2026-45028 is a low-severity cross-site scripting (XSS) vulnerability in astro (npm), affecting versions < 6.1.10. It is fixed in 6.1.10. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-45028? CVE-2026-45028 has a CVSS score of 6.1 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of astro are affected by CVE-2026-45028? astro (npm) versions < 6.1.10 is affected.
4. Is there a fix for CVE-2026-45028? Yes. CVE-2026-45028 is fixed in 6.1.10. Upgrade to this version or later.
5. Is CVE-2026-45028 exploitable, and should I be worried? Whether CVE-2026-45028 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-45028 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-45028? Upgrade astro to 6.1.10 or later.